One of the challenges facing telecommunication providers is that existing networks are continuously needing to be updated, in order to keep up with ever increasing customer demands and anticipated future demand including the demand for increased data transmission speeds and capacity. One area of technology that has been increasingly used to keep up with customer demand is the use of optical signal transmission equipment.
Beneficial features associated with the use of optical signal transmission, including the type of transmission used in fiber-optic systems, has led to their increased use in the design and implementation of communication networks. One of the benefits of optical signal transmission is the distance an unamplified optical signal can travel prior to being received. Existing glass fiber, and corresponding system electronics, enable digitized light signals to be transmitted 100 km or more without amplification. A further benefit of optical signal transmission is the volume bandwidth of traffic that can be routed through a single signal carrying connection, like an optical fiber. Data rates of up to 10 Gbps at a single wavelength are routinely possible. Systems are available, which can support 150 or more wavelengths.
One of the earlier hurdles to designing networks incorporating early generations of fiber-optic systems, integrated as part of the public telephone network, involved the extensive use of proprietary architectures by equipment manufacturers including corresponding proprietary hardware and communication protocols. The proprietary architectures limited the ability of network users and designers, like Bell operating companies and inter-exchange carriers to integrate equipment from different suppliers into their systems, when developing or updating a network. This significantly limited the designers choices and options in terms of equipment and features after an initial proprietary scheme was selected to the available features incorporated into the equipment compatible with the proprietary scheme. In many cases this limited the network designer to equipment produced or supplied by a single vendor. As a result, it became desirable to develop a standard for which multiple manufacturers of optical network equipment could supply compatible products. One such standard for optical telecommunications transport, which was developed, is the SONET/synchronous digital hierarchy.
SONET stands for Synchronous Optical NETwork, and was formulated to provide a standard, comprehensive, synchronous digital hierarchy, which includes an optical hierarchy on top of an already existing electrical hierarchy. Furthermore this standard opened up the possibility of acquiring equipment manufactured by multiple suppliers, and integrating such diverse equipment into the same network.
As optical networks have begun to shoulder an increasing portion of the network traffic, general design principles applied to the communications systems are being more rigorously applied to the optical hierarchy layer of the communication network. One of these design principles is a desire for network survivability should a network component fail.
Traditional approaches to network survivability have included the use of redundant signal paths and equipment, and the ability to automatically reroute traffic in the event of a network failure. As a result previous point-to-point optical networks have increasingly given way to ring-based networks, which have certain inherent self-healing properties.
In a ring-based network the locations or nodes are arranged in a closed loop sequence. The last node in the sequence is connected to the first node in the sequence.
One or more of these rings or cycles are defined for a given set of locations or nodes. In a ring-based network, the locations located on a given ring, are inherently biconnected. This means that between any two locations two disjoint signal paths exist between them. More specifically in a SONET-based ring network a clockwise path and a counter-clockwise path generally exist. In SONET-based ring networks a service fiber traditionally transmits traffic data in one direction, while a protection fiber transmits traffic data in an opposite direction.
In networks where multiple rings are defined, redundant signal paths for traffic communications between rings and corresponding locations on each of the respective rings can be met by incorporating dual-homed rings or rings that are biconnected to at least one of the other defined rings. In other words, the two rings have at least a pair of common locations present on both of the rings through which traffic can be routed. In this way, should the communication equipment associated with one of the shared locations fail and no longer be able to communicate signal traffic between rings at that location, the communication equipment at the second shared location is available for alternatively routing the traffic data between the rings.
However as the number of locations and the corresponding amount of network traffic traveling between locations increases, decisions as to how to define the rings and how to deploy the communication equipment in an efficient and a cost effective manner can become quite complex. As a result, it would be beneficial to develop a structured method and system for systematically designing relatively efficient ring-based telecommunications networks.